His comments came after UK media reports said police were seeking a British man who had been travelling with Miller in connection with the killings.

Panya could not confirm Thai television reports that police had seized an iPhone and blood-stained jeans after raiding rooms used by the Myanmar suspects.

Thai authorities frequently accuse migrants from Myanmar and Cambodia of committing crimes in the kingdom, where they make up a vast, poorly-paid and low-status workforce.

The bodies of the victims, who arrived in Thailand on August 25, are due to arrive in Bangkok later Tuesday for forensic tests, said local police official Jakkrapan Kaewkhao.

- 'Affected our image' -

Koh Tao, home to stunning white sand beaches and azure waters, is popular with divers but is smaller and more laid-back than neighbouring Koh Phangan -- which draws hordes of backpackers to its hedonistic "full moon" party.

On Tuesday Thai junta chief and prime minister Prayut Chan-O-Cha appeared to call into question the victims' conduct in addition to the perpetrators of the attack.

"We have to look into the behaviour of the other party too because this kind of incident should not happen to anybody and it has affected our image," he told reporters, referring to the two tourists.

Police earlier said the pair had been seen partying at a local bar just hours before they died.

The murders are likely to heap more misery on Thailand's lucrative tourism industry, which has been battered in recent months after a prolonged political crisis ended in a coup.

The army swiftly blanketed the country with a curfew and strict martial law, frightening off visitors.

Although the curfew was soon lifted from key tourist hotspots, visitor numbers have yet to rebound and martial law remains in place.

Military leaders have vowed to restore the nation's reputation as the "Land of Smiles" with a clean-up targeting tourist resorts after a series of complaints about scams, assaults and even police extortion.

Britain says Thailand is the country where its citizens are second most likely to require consular assistance if they visit, behind the Philippines.

There were 389 deaths of British nationals in Thailand in the year to March 2013 -- about one for every 2,400 British visitors or residents -- although that figure includes natural causes.

But it is rare for tourists to be murdered in Thailand, although it is not uncommon for visitors to die accidentally.

In July last year a 51-year-old American tourist was stabbed to death after an apparent row in a bar in Krabi, another popular tourist haven.

His death came just weeks after another American was slashed to death by a taxi driver in Bangkok after an apparent argument over the fare.